My family had great plans for the holiday weekend but, fortunately, the poor weather forecast came to my rescue and I was able to take a day out to construct the extension to my laser tube enclosure. This did not exactly go down too well with them but they now have my full attention for the next couple of days.

The new tube will sit on the two existing mountings, held in position by the elastic bungee cords and the laser beam will exit through the small hole in the far end of the enclosure. Although the mountings are adjustable, from underneath, I am hopeful that the alignment will not be too much of a drama.

Have you ever tried to vary the power of any of your lasers with analog modulation to engrave a picture with g-code in Mach3 to get shades instead of pulsing your laser to get the allusion of shades? I have perfected a process to do it using PhotoVcarve software and an absolute shaft encoder with analog 0-5V output.

I have been following your progress on the Vectric forum with great interest - Very nice work you are producing.

Art's Mach3 Impact / Laser plugin does just as you describe, producing the shades of gray by a PWM method of varying the laser on time. This is OK for certain materials (such as wood) but many other materials just do not accept shade.After many trials and comparisons I prefer the half-tone method but, as you have shown, each method has it's own merits.

Tweakie.

Logged

Success consists of going from failure to failure without loss of enthusiasm. Winston Churchill.

I do have to say though, technically by using PWM in Art's plugin is still pulsing the laser on and off to get shades. It's not really varying the power like I am with the MA3 analog absolute encoder and the PhotoVcarve software. My laser never turns off until the engraving is finished.

I have one of these driving the 445nm laser diode. http://hacylon.case.edu/ebay/laser_diode/FlexModP3.php. It has analog and TTL modulation I'm using the USB port to power one of these. http://usdigital.com/products/encoders/absolute/rotary/shaft/MA3 I purchased the analog output version instead of the PWM output one and it's attached to the Z axis stepper motor by a timing belt and pulley setup with a 6-1 ratio. With these ratios, when my Z axis motor moves from Z0.00 to Z-.016" the encoder outputs 0-5V. With a 2-1 ratio to my Z axis screw the laser only moves .008" and it's not enough to go out of focus. I'm not using any special code, but just like the PhotoVcarve software outputs for a Lithophane or rotary bit engraving with the X Y & Z g-code moves. Darker areas with a deeper depths of cut, it throttles up the power of the laser and lighter areas it throttles back so it is truly variable and proportional with all shades in between. This could be done with a more powerful CO2 laser if there was a way to vary the output power of it. I was planning on down the road to build my larger CNC router into one, when my finances with allow. I guess the tube would have to be mounted vertically to make it work properly. That way it could still move up and down based on material thickness so the beam would still stay in focus.

Based on the excellent results Jeff (JJWMACHINECO) has achieved with burning ‘shades of grey’ into wood…

There are those that have converted imported CO2 laser machines to operate with Mach3 who do not actually have a motorized Z Axis and others who perhaps do not wish to add an encoder to their existing Z Axis. For this scenario I submit the following design idea which is primarily aimed at CO2 lasers with 40 Watts (or more) available output power.

Because the Mach3 internal PWM generator cannot easily be controlled ‘on the fly’ with the S*** commands blended with X Axis movement, or at least not fast enough to be useful, another approach has been considered.

It is perfectly feasible to construct a ‘stand alone - step / direction’ controlled PWM generator the output of which is easily converted to a voltage with a simple DAC (digital to analogue converter). Then by using 2 voltage dividers, one to set the lower voltage at which the wood is just marked and the other to set the higher voltage at which the maximum burn is achieved the laser output power can be fully controlled (via its PSU), with 8 bit resolution, from a lithophane type GCode tool-path.

I threw out the initial idea of connecting an encoder to a stepper motor and then using a standard stepper motor driver in favour of an all electronic solution which will enable ‘on the fly’ adjustment of the minimum and maximum thresholds whilst still maintaining an 8 bit resolution of voltage over a typical 2mm depth of tool-path.

My design may well be a bit theoretical at this stage but so far I have established that a PIC microprocessor, clocked at 20MHz, can be configured within Mach3 as an Axis which can then be driven at a typical feed-rate of 1000mm/min with 127.5 steps/mm and produce a continuously updated PWM output between 0 and 100%.Referring to my very basic schematic, this PWM is then opto-isolated, to remove the GND constraint and place the 255 step output potential between the maximum and minimum voltage settings of the two potential dividers. A simple DAC is then used to drive the emitter-follower output voltage to the laser PSU.

For the initial testing and for convenience, I am using a partially populated pcb from my RF Laser controller design (mentioned many posts back) purely because the display is useful, at the software design stage, to be able to observe the various settings and values. The final design will be a lot less complicated.

Can't wait to see some pictures with shades you engrave using that setup. I'm getting allot better and consistent results with John's PicEngrave Pro software then before using PVC. Here is one I did the other day and the detail is amazing.